The invention relates to a method for the testing of packs of formable packaging material, especially of (cigarette) packs having at least one wrapper of (thin) cardboard. The invention also relates to an apparatus for implementing the method.
The testing of packs is particularly important in the manufacture of cigarette packs, which requires a high degree of precision.
The invention is based on the problem of suggesting measures for implementing a precise testing of packs which can also be executed in a simple manner.
For solving this problem, the method according to the invention is characterized in that the pack is impinged by a defined or measured pressure, giving rise to deformations which are then measured and evaluated.
Essential to the invention is the knowledge that the progression of the deformation caused by pressure on the pack is characteristic for its construction and also for its contents. Furthermore, certain features of its construction and design can be identified by its deformation curve.
According to the invention, the course of pack deformation is determined by changes in the force applied for deformation with respect to a preset default deformation curve. In actual practice this means that a pressure-exerting means acting on the pack is measured with respect to the distance covered and the force occurring during the deformation process. The measured results are recorded and evaluated on a continual basis, in particular by graphic representation. This result of evaluation is displayed on a computer as a curve plotting the variables of force and distance. The pressure-exerting means is preferably pressed against or set upon the pack with uniform, in particular, constant movement. The force resulting from the pack""s resistance is measured and plotted over the distance.
One special feature of the invention ties it the knowledge that, during the deformation process, a change in the measured force occurs a number of times, specifically as a result of the pack""s structural details. In an advantageous exemplary embodiment, namely when testing a cigarette pack of the hinge-lid type, the force applied during the deformation process is recognizably influenced by structural details such as lid inner tabs, transverse edges at the lid end as well as at the bottom end, generating in the graphic recording of the force curve a typical and reproducible image of the deformation behavior of the pack.
The recorded and graphically displayed results of measurement can, according to the invention, be compared with a reference curve or a stored xe2x80x9ccalibration curvexe2x80x9d in order to identify any deviations from a standard embodiment of the pack concerned. One special feature lies in the fact that for this purpose the second derivative of the force/distance curve is determined and recorded. The resulting curve exhibits elevated curves or peaks which correspond to an increased force or increased pack resistance to deformation, thus enabling one to draw conclusions concerning the construction as well as the material composition, material strength and the pack contents.
The present measuring and testing method can be applied with particular advantages to cigarette packs of the hinge-lid type, i.e. to a pack made of thin cardboard. The pack is tested after it is finished, either before or after it is surrounded by an outer wrapper of film.
For implementing the method according to the invention, the pack is clamped as a whole between pressure-exerting means which are displaceable relative to one another, namely in particular between an (upper) pressure plate and a (lower) plate-shaped load cell. At least one means is displaceable. The path traveled is measured as well as the attending force. This yields the characteristic deformation behavior of the pack.
Method and apparatus can be integrated in a packaging process, preferably by positioning a test station in the region of a pack conveyor, with pack samples being removed from the conveying stream and tested for their correct shape.
Further special features of the invention are explained below in more detail by means of an exemplary embodiment of an apparatus and by means of the evaluation procedure. Shown are: